NUCLEIC ACIDS AND SULPHYDRYL GROUPS
269
of one specific amino-acid might be the limiting factor in this system.
Another possibility, which involves the various forms of RNA's, will be
presented later.
Regarding enzymes, i.e., specific proteins, our colleague, E. Baltus
(1959) was the first to demonstrate that anucleate fragments of Acetabularia are capable of autonomous synthesis of aldolase. This enzyme
does not show a preferential localization in a given type of particle after
homogenization and differential centrifugation. Similar results have
been obtained for Phosphorylase and invertase (Hämmerling et al., 1959).
The synthesis of these three enzymes is parallel to that of the total
protein: it stops 3 weeks after removal of the nucleus. But a different situation is found in the case of acid phosphatase, the synthesis
of which is completely and quickly arrested in the absence of the nucleus
(Keck and Clauss, 1958). It is interesting that a comparable behaviour
of acid phosphatase also occurs in anucleate amoebae (Brächet, 1955)
in which removal of the nucleus exerts relatively little influence on the
activity of most enzymes, but in which acid phosphatase and esterase
(as well as RNA) quickly and considerably decrease. These results
suggest that, for reasons which will be presented later, acid phosphatase
(and possibly esterase) lie under a much closer nuclear control than the
total proteins and other enzymes.
The work of Keck (1960) concerning the nuclear control exerted on
acid phosphatase, is also of great interest. He found that this enzyme is
electrophoretically different in Acetabularia
and in a related genus,
Acicularia.
The anucleate fragments produce the enzymes for only a
very few days, and their synthesis then completely stops. If an Acetabularia nucleus is grafted to an Acicularia cytoplasm, the
Acicularia
acid phosphatase activity vanishes within 5 days, while it remains
present in anucleate fragments of Acicularia for 20 days. The converse
experiment, i.e., the graft of an Acicularia rhizoid onto an anucleate
stalk of Acetabularia,
gives a surprising result : only the
Acetabularia
enzyme is detectable. Finally, binucleate grafts between the two species
have been made by Keck (1960); again, only Acetabularia enzyme can
be found in the vegetative hybrid. These experiments clearly show that,
in the case of acid phosphatase synthesis, Acetabularia is dominant over
Acicularia.
We have been dealing so far with nuclear control of protein synthesis
in Acetabularia. A few words should now be said about another part of
the alga which is very important for morphogenesis, the apex of the
stalk (where the cap will form). Cytochemical work by Werz (1959) has
shown that, in growing algae, special proteins can be detected in this
apical part of the alga. These proteins, which stain with azocarmine Β
at pH 2, are absent in algae which do not grow, or are kept in darkness.
269
of one specific amino-acid might be the limiting factor in this system.
Another possibility, which involves the various forms of RNA's, will be
presented later.
Regarding enzymes, i.e., specific proteins, our colleague, E. Baltus
(1959) was the first to demonstrate that anucleate fragments of Acetabularia are capable of autonomous synthesis of aldolase. This enzyme
does not show a preferential localization in a given type of particle after
homogenization and differential centrifugation. Similar results have
been obtained for Phosphorylase and invertase (Hämmerling et al., 1959).
The synthesis of these three enzymes is parallel to that of the total
protein: it stops 3 weeks after removal of the nucleus. But a different situation is found in the case of acid phosphatase, the synthesis
of which is completely and quickly arrested in the absence of the nucleus
(Keck and Clauss, 1958). It is interesting that a comparable behaviour
of acid phosphatase also occurs in anucleate amoebae (Brächet, 1955)
in which removal of the nucleus exerts relatively little influence on the
activity of most enzymes, but in which acid phosphatase and esterase
(as well as RNA) quickly and considerably decrease. These results
suggest that, for reasons which will be presented later, acid phosphatase
(and possibly esterase) lie under a much closer nuclear control than the
total proteins and other enzymes.
The work of Keck (1960) concerning the nuclear control exerted on
acid phosphatase, is also of great interest. He found that this enzyme is
electrophoretically different in Acetabularia
and in a related genus,
Acicularia.
The anucleate fragments produce the enzymes for only a
very few days, and their synthesis then completely stops. If an Acetabularia nucleus is grafted to an Acicularia cytoplasm, the
Acicularia
acid phosphatase activity vanishes within 5 days, while it remains
present in anucleate fragments of Acicularia for 20 days. The converse
experiment, i.e., the graft of an Acicularia rhizoid onto an anucleate
stalk of Acetabularia,
gives a surprising result : only the
Acetabularia
enzyme is detectable. Finally, binucleate grafts between the two species
have been made by Keck (1960); again, only Acetabularia enzyme can
be found in the vegetative hybrid. These experiments clearly show that,
in the case of acid phosphatase synthesis, Acetabularia is dominant over
Acicularia.
We have been dealing so far with nuclear control of protein synthesis
in Acetabularia. A few words should now be said about another part of
the alga which is very important for morphogenesis, the apex of the
stalk (where the cap will form). Cytochemical work by Werz (1959) has
shown that, in growing algae, special proteins can be detected in this
apical part of the alga. These proteins, which stain with azocarmine Β
at pH 2, are absent in algae which do not grow, or are kept in darkness.